Historical biology and the problem of design

Organisms are historical entities in that their past history plays an important role in shaping the properties they exhibit today. While this fact is widely acknowledged, little attempt has been made to develop a testable approach to the analysis of the historical factor in evolutionary morphology. The analysis of extrinsic environmental factors may reveal the limits imposed by the environment on biological design, but the intrinsic phylogenetic component of design may severely constrain the directions of structural modification that can occur. The importance of history can be assessed with (1) a phylogenetic hypothesis of genealogical relationship, (2) the use of emergent structural or functional attributes with general properties, and (3) the testing of historical hypotheses by the comparison of general properties between monophyletic lineages. The synthesis of a structural/phylogenetic approach to historical morphology with the analysis of extrinsic limits to form may provide the level of resolution needed to generate testable mechanistic hypotheses regarding the distribution of extant organismal forms in the hyperspace of possible morphologies.